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DESCRIPTION OF THE ORE OCCURRENCES

The main outcrops of the magnetite ore-bodies of the Prescott mine
(See Figure 16) occur on a hill-side about 600 feet from the seashore and at
elevations of 400 to 600 feet. The ore-bodies occur at the contact of
limestone and quartz diorite and lie mainly within an area of much altered
quartz diorite. The upper slopes are underlain by limestone. On the
lower slopes of the hill, away from the ore-bodies, the quartz diorite is a
normal, unaltered rock, but approaching the ore-bodies it shows many signs
of alteration and in the immediate neighbourhood of the ore masses the
diorite is largely replaced by secondary minerals such as epidote and mag-
netite. In places the rock is so rich in magnetite, occurring either irregularly
distributed throughout it or in part concentrated in masses, some of large
dimensions, as to constitute what might be termed a low-grade iron ore.
Within the area of most highly altered diorite occur the ore-bodies, con-
sisting mainly of magnetite but accompanied by various silicates and by
masses of incompletely replaced rock. In one instance, an ore-body
occurs resting on limestone.

The ore masses have been partly developed and worked by open-cuts
and by a long tunnel entering the hill-side at an elevation of 165 feet and
ending at a point nearly beneath one of the large ore-bodies visible on the
surface. At an elevation of about 490 feet, a quarry face has been opened
with a length in an east and west direction of 100 feet. The quarry is
open to the south. The north wall rises steeply for 70 feet or more and
consists of limestone and irregular bodies of magnetite, in part connected
with one another, in part in isolated masses, and they vary in size from such
as are small patches to others several or more yards in width. No attempt
has been made to mine these masses; they give no evidence of forming
bodies of size large enough to warrant mining and possibly are only root-
like projections of a once continuous mass since removed by mining. At
the summit of the eastern part of the quarry face, at an elevation of 70 to
90 feet above the quarry floor, magnetite outcrops over an area about 100
feet long by 40 feet broad. This mass is a remnant of a body of ore which
in times past afforded much of the ore shipped. At one time it apparently
extended down to the quarry floor, and rested on the steeply inclined
face of limestone now forming the wall of the quarry (See Figure 16,
section F-G). The body of ore still remaining appears to be a shallow
mass presumably nowhere much more than 10 feet thick.

At its western end the quarry working extends into a southward
projecting spur of the hill, so that there are rock faces on the north, west,
and south sides. The limestone forming the north wall of the quarry
extends into the west part, but is there replaced by altered diorite. The
two rocks are in sharp contact, divided by a nearly vertical plane. To
the west, after a space of a few feet, the altered diorite is succeeded by
still more highly altered diorite impregnated with much magnetite. This
more highly altered rock occupies the west and south face of the pocket-
like extension of the quarry and with a width of about 50 feet extends
westward upward and over the ridge dividing the quarry from a second
open working yet to be described. On the west face of the pocket-like
extension of the quarry, the rock face for a breadth of about 25 feet at
the level of the quarry floor is occupied by ore and this mass extends up
the nearly vertical west quarry face to an estimated height of 30 feet.